Hydraulic cushion for die pads in presses



March 1964 F. M. WILLIAMSON HYDRAULIC CUSHION FOR DIE PADS IN PRESSES 2 Sheets-Sheet 1 Filed Oct. 8', 1962 INVENTOR M Miizkrrzsor;

March 10, 1964 M. WILLIAMSON 3,

HYDRAULIC CUSHION FOR DIE PADS IN PRESSES Filed Oct. 8, 1962 2 Sheets-Sheet 2 QZ K INVENTOR.

United States Patent Oflice 3,124,343 Patented Mar. 10, 1964 3,124,343 HYDRAULIC CUSHION FOR DllE PADS HQ PRES ES Floyd M. Williamson, Di-Dro Engineering (10., 2M5 E. Grand Blvd, Detroit 11, 'Mich. Fiiedflct. 8, 1962, Ser. No. 229,138 11 Claims. (Cl. 267-1) This invention relates to hydraulic cushions for dies and die pads in mechanical presses and has particular reference to systems of the type disclosed in my prior Patent No. 2,901,238, issued August 25, 1959, wherein the hydraulic cushion controls the retraction of a die or die pad upon the closing of the press ram and returns the die or die pad to its extended position after opening of the press ram. Hydraulic cushions embodying the invention herein disclosed and claimed are particularly adapted for controlling the movement of dies and die pads in mechanical presses during the closing and opening movements of the press ram.

In hydraulic cushions-incorporating the invention, the system is normally maintained under a relatively low pressure, say for example 100 pounds per square inch, and includes means eifective to provide a controlled high pressure resistance to'the closing of the press ram and for cetain requirements, and means to delay or retard the return movement of the die pad to its extended position upon the opening of the press ram.

The invention is particularly directed to the valve means which controls the flow of hydraulic fluid to and from the high pressure side of the hydraulic cushion. Because of the high pressures which are rapidly generated in hydraulic cushions during the closing of the press ram, the adverse effect of heat generated in the hydraulic fluid used, and the desirability of high speed press operation consistent with the limitations necessarily imposed by the drawing operations being performed, the requirements for the valves used in such hydraulic systems to provide a high pressure resistance to the discharge of hydraulic fluid from the high pressure side of the cushion during closing of the press ram are very servere. The invention herein disclosed is directed toward certain improvements in the valve and its relation to the system designed to more efiiciently control the discharge of hydraulic fluid from the high pressure side of the cushion during the closing of the press ram so as to improve the performance of the hydraulic cushion and the drawing operations of the press.

A principal object of the invention, therefore, is to provide an improved hydraulic cushion for die pads in presses.

Another object of the invention is to provide a new and improved pressure regulating valve means for hydraulic cushions.

Other and further objects of the invention will be apparent from the following description and claims and may be understood by reference to the accompanying drawings, of which there are two sheets, which by way of illustration show preferred embodiments of the invention and what I now consider to be the best mode of applying the principles thereof. Other embodiments of the invention may be used without departing from the scope of the present invention as set forth in the appended claims.

In the drawings:

FIG. Us a schematic illustration of a hydraulic cushion embodying the invention;

FIG. 2 is a schematic view illustrating a modified form of the invention incorporating means to delay return movement of the die pad;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2;

FIG. 4 is a fragmentary sectional View illustrating a modification of the invention as illustrated in FIG. 3; and

FIG. 5 is a fragmentary sectional view illustrating a further modification of FIG. 3.

As schematically illustrated in FIG. 1, a mechanical press having a reciprocating ram It and a bolster 12 is provided with a die pad l iwhich engages the work blank and is retracted upon the closing of the press ram. The hydraulic cushion includes a cylinder 16 and a piston 18 which react on the die pad 14 to resist the retractile movement thereof during the closing of the press ram and to return the die pad to its extended position after opening of the press ram. One or more cylinders and pistons may be used.

A tank 29 of hydraulic fluid is maintained under a controlled relatively low pressure, say for example pounds per square inch. Hydraulic fluid flow and pressure transmitting connections extend between the tank 20 and the cylinder 16 which is on the high pressure side of the cushion for supplying hydraulic fluid under tank pressure to the cylinder 16 when the tank pressure exceeds that of the cylinder 16, and a normally closed valve means indicated generally at 22 is incorporated in such hydraulic connections so as to provide a high pressure resistance to the discharge of hydraulic fluid from the cylinder 16 during closing of the press ram, the valve means being constructed and arranged so as to permit free flow of hydraulic fluid from the tank 2% through the valve means to the high pressure side of the cushion when the tank pressure exceeds that of the cylinder 1-6 which occurs during the opening of the press ram.

The hydraulic fluid connections include the hydraulic line 24- which extends from the valve means 22 to the cylinder 16 and the hydraulic line 26 which extends from the valve means 22 to the lower end of the tank 26}. The valve means generally includes a normally closed combined check and pressure relief valve 30, a spool type control valve 32, and a normally closed pilot relief valve 34, these valves being incorporated in a valve body comprising blocks 36 and 3 suitably secured together. The block 3-5 is provided with a cylindrical bore 40 in one end of which valve cylinder element 42 is seated and confined by annular valve seat member 44 which is seated in the other end of the bore 40 adjacent the block 38. The valve seat member 44 is centrally apertured to provide a central port and annular valve seat 45 which communicates through passage 4% with the hydraulic line 26. The valve seat member 44 forms one end wall for a cylindrical valve bore 5t) formed in the element 42, the end of the element 42 which defines the bore 50 being provided with a series of lateral ports 54 which afford communication between one end of the valve bore 5%? and the outer cylinder bore 40. The cylinder bore do in turn is provided with a port in the side wall thereof which communicates by means of passage 56 with the hydraulic line 24.

The combined check and pressure relief valve 3% is a piston valve which is slidable in the bore 5% between closed position as shown and open position so as to control fluid flow through the bore 5i; between the lateral ports 54 and the central port 46 in the end wall. Piston valve 3t? includes a frusto-conical portion which seats on the port seat 46 so as to close the communication between the interior of the bore 5d and the passage 43. The piston 36 includes a cylindrical portion or piston 58 of reduced diameter which is reciprocable in a cylinder 64) also formed in the element 4 2, and a coil spring 62 confined between the end face of the piston 58 and the closed end wall of the cylinder bore 4t) biases the piston valve 3% to its closed position as shown.

A hydraulic fluid flow connection 64 extends between the cylinder 60 and the passage 56, and a hydraulic fluid flow connection 66 extends between the cylinder 60 and the passage 48. Control valve bore 63 intersects the connections 64 and 66, and reciprocable spool valve 32 is arranged in the bore 63 so that one of such connections is open while the other is closed, the valve 32 normally being positioned by a spring 71 so as to close the connection 64 between the cylinder 60 and port 56. The opposite end faces of the spool valve 32 are exposed through passages 72 and 74 to the hydraulic fluid pressure in the tank and in the cylinder 16 so that the spool valve 32 will be positioned as illustrated by the pressure of the fluid on the high pressure side of the hydraulic cushion when it is above tank pressure, and in the opposite position under the reverse pressure conditions. However, the spring 71 normally biases the valve 32 so that the connection 66 is open between the cylinder 60 and the tank, and the connection 64 between the cylinder 60 and the cylinder 16 is closed. When the pressure in the cylinder 16 of the hydraulic cushion is below tank pressure, tank pressure will shift valve 32 to close the connection 66 and open the connection 64 so that the valve 30 is then free to open under the pressure in the tank 20 and against the spring 62 to permit the free flow of hydraulic fluid from the tank side of the valve to the cylinder side of the valve for recharging cylinder 16 and biasing the piston 18 to its extended position.

A restricted flow passage 76 is provided between the cylinder 46 and the bore 50 on the back side 78 of the valve 30, and a fluid flow pressure relief passage 80 of substantially greater cross section than passage 76 extends between the bore 50 on the back side 78 of the valve 30 and the passage 66, the end of the passage 80 which intersects the passage 66 defining a valve seat on which the pilot pressure relief valve 34 seats so as to normally close the pressure relief passage 80. The passage 66 extends through the bore 82 in which the valve 34 is reciprocable, and a coil spring 84 reacts against valve 34 so as to maintain it normally closed, the spring 84 being backed up by an abutment 86 which in turn is backed up by the threaded adjusting screw 88 whereby the pressure on the spring 84 may be varied and hence the pressure at which the valve 34 will open may be regulated. The valve 34 is adjusted so as to open at a predetermined high pressure so as to develop the desired resistance to the discharge of hydraulic fluid from the cylinder 16 during the closing of the press ram.

The valve 34 functions as a pilot relief valve and, when open, relieves or dissipates hydraulic fluid pressure on the back side 78 of the piston valve 30 (due to the restriction afforded by passage 76) when the hydraulic pressure on the high pressure side of the valve 30 rises substantially above tank pressure due to closing of the press ram so as to cause the piston valve 30 to shift to its open position and thus permit the fiow of hydraulic fluid between the valve bore ports 54 and 46 and through the valve bore 50 from the high pressure side of the piston valve to the tank side thereof. In this way the valve 30 functions as a pressure relief valve.

The light spring 62 biases valve 30 to its closed position, and is the only force which holds valve 30 in its closed position. The pressure responsive surfaces of valve 30 preferably are such that the axial pressures exerted on the valve by the hydraulic fluid on the high pressure side and the hydraulic fluid under tank pressure are balanced and do not bias the valve 30, regardless of the considerable fluctuation in pressure on the high pressure side relative to the controlled or fixed tank pressure. Thus only a light spring 62 is required to seal the valve and only a light force is necessary to overcome the spring 62 to open the valve 30.

Assuming that the system is charged with hydraulic fluid under tank pressure and that the piston 18 is in its extended position, the closing of the press ram will react on the piston 18 in a direction to move the piston to its retracted position. As the valve 30 is closed, hydraulic fluid is trapped on the high pressure side of the valve 30 and thus the pressure of such fluid will rise rapidly until it reaches a value sufficient to unseat the pilot relief valve 34. When the pilot relief valve 34 opens, the pressure in the bore 50 on the back side 78 of the valve 30 will be suddenly released and drop due to the restricted passage 76 between such part of the bore 50 and the bore 40, thus reducing the pressure on the annular sur- 'face 78 whereby the high pressure on the opposite side of the valve acting on the conical surface of the valve 30 outwardly of the port 46 will shift the valve 30 to open position and permit the flow of high pressure fluid at the desired pressure from the end of the bore 50 through port 46 into the passage 48. Thus the valve 30 provides a high pressure resistance to the discharge of hydraulic fluid from the high pressure side of the hydraulic cushion during the closing of the press ram. The resistance thus aflorded may be regulated by rotation of the adjusting screw 88. As the valve 32 at such time is in the position as illustrated in FIG. 1, hydraulic fluid in the cylinder 60 will be freely displaced by the opening movement of the valve 30. As the ram approaches its fully closed position after opening of valve 30, the rate of displacement of fluid from the cylinder 16 will decrease due to the deceleration of the ram, and valve 30 will thus move toward its closed position and close when the ram has reached the bottom or end of the power stroke and the pressure on the high pressure side drops below the setting of valve 34.

As the ram begins its upward stroke, the pressure generated thereby in the hydraulic fluid in cylinder 16 will rapidly drop below the tank pressure, whereupon the hydraulic pressure on the tank side of the valve 30 will shift the valve 32 to its other position and thus reduce the hydraulic pressure on piston 58, permitting tank pressure to unseat the valve 30 and thus permit the flow of hydraulic fluid through the valve port 46 from the tank to the other side of the valve 30 so as to recharge the hydraulic cylinder and thereby return the die pad to its extended position. When the hydraulic cylinder 16 is recharged by the tauk pressure, the spring 71 will shift the valve 32 to its position as illustrated and hydraulic fluid under tank pressure will recharge the cylinder 60 and react on the piston 58 so as to enable the spring 62 to seat the valve 30.

In the modification of FIGS. 2 and 3, means are provided to delay the recharging of the cylinder 16 until after the press ram begins its upward stroke. As shown in FIGURE 2, valve 30 preferably includes a pilot 31 slidable in port 46 to guide valve 30 at is opens and closes, the pilot 31 being provided with one or more diametral V-shaped notches 33 which form fluid flow ports as the valve 30 opens. This could be used in the valve of FIG- URE 1. Except for these features, the construction and operation of the valve means as shown in FIGS. 2 and 3 are the same as in FIG. 1, and accordingly only the construction and operation of these additional features will be described. Like reference characters are used in FIGS. 1, 2 and 3 to indicate like parts.

As shown in FIGS. 2 and 3, a valve bore intersects passage 72 and a spool valve 102 is reciprocable in such bore so as to block the flow of hydraulic fluid from the passage 66 through the passage 72 when the valve 102 is positioned as illustrated so as to delay opening of valve 30. The valve 102 is biased by spring 104 to an open position so as to bring annular groove 106 of the valve 102 into registry with the passage 72 so as to permit the application of hydraulic fluid under tank pressure to the end of valve 32 for shifting it to its other position when the pressure on the high pressure side of valve 30 is below tank pressure. Spring 104 is backed up by a slidable abutment 108 which is positioned by a threaded pin 110 whereby the force exerted by spring 104 on the valve 102 may be adjusted for the purpose of regulating the time interval of the delay in opening valve 30 and recharging of cylinder 16. It will be appreciated that when the valve 30 closes after the ram has reached the bottom of its power stroke and the pressure on the high pressure side drops below the setting of valve 34, the valve 39 cannot be opened by the tank pressure until the control valve 32 has shifted to its other position so as to eliminate tank pressure from the end face of the piston 58. With the valve 102 positioned as illustrated in'FIGS. 2 and 3, tank pressure will be ineffective to open the valve 30 since tank pressure is being applied to the piston 58.

During the closing of the press ram, high pressure fluid from the high pressure side of the valve 22 will be conducted by passages 112, 114 and 116, andalso through passages 118 and 120, into the spaces formed by the annular grooves 122 and 124 formed by the bushing 126 disposed in the bore 123. Check valve 119 in an enlarged portion of the passage 118 permits free flow of hydraulic fluid from passage 116 through passage 118 and passage 121) while preventing reverse flow through passage 113.

The interior of the bushing 126 provides a cylinder for the-end 13d of the valve 102, and with the end 13% of the valve 1&2 seated against the end wall of the bore 128 under the influence of spring 164, hydraulic pressure fluid from the high pressure side of the valve will be supplied through the passages 116 and 120, the grooves 122, 123 and 124, and the passages 125 and 127 in the end of the piston 13% to the upper or closed end of the bore 123 sons to react on'the valve 1% and shift it from its open to its closed position as illustrated, thus blocking the passage 72 and temporarily preventing tank pressure from shifting the valve 32 to its other position.

Under the influence of the spring 104 the valve m2 is biased to its open position, and thus the fluid trapped between the end 13% of the valve 1%2 and the closed end of the bore 128 will be displaced through the metering orifice formed between the end of the metering pin 132 and the end of the passage 112% remote from the bore 128. The metering pin 132 is formed on the end of a threaded member 13 5 having a kerf 136 in the head thereof whereby the metering orifice may be adjusted so as to regulate the escape of hydraulic fluid from the closed end of the bore 123 under the influence of the spring 104. Valve W2 moves toward its open position until groove 123 registers with passage 125. The remaining hydraulic fluid trapped in the valve structure then flows through passage 127, groove 123, passage 125, and groove 122 to passage 116 thereby bypassing metering pin 136) and allowing annular groove 1% to move across and rapidly open passage '72.

The passage 112 communicates with a cross bore 140 which communicates through connection 64 with passage 56 on the high pressure side of the valve. A passage 142 having a check valve 144- therein communicates at one end with the passage '72 between the valve bore 1% and the end of the valve bore 63, and at the other end with passage 645 so as to prevent hydraulic fluid from being trapped in the passage '72 if the valve 1&2 is in its closed position as shown. Thus, when the valve 3%) closes after the ram has reached the bottom of its power stroke, the valve 162 will be closed by hydraulic fluid from the high pressure side of the valve fat so as to prevent the reopening of the valve 3@ for a desired time interval after the ram begins its upward stroke. After the valve 162 shifts to permit opening of valve 30, the cylinder will be recharged with fluid under tank pressure and the die pad will be moved to its extended position as described in connection with the modification of FIG. 1. In some cases it is desirable to delay the return of the die pad to its extended position until after the ram has moved upward away from the work. The pad delay valve 102 functions so as to permit the return of the die pad 14 to its extended position under tank pressure, even after motion of the press ram ceases, because the opening of valve 192, as per FIGS. 2 and 3, is not dependent upon press operation.

Instead of hydraulically shifting the valve 102 to its closed position as illustrated in FIG. 3, the valve 102 may be shifted to its closed position by the core 151 of a solenoid 15'6, the circuit of which is controlled and periodically closed by a cam 152 which is rotatable with the crank of the press. Thus the valve 102 of FIG. 4 is normally open and shifted to a closed position upon the energization of the solenoid just before the press ram begins to move upwardly so as to temporarily delay the opening of the valve 39 after the press ram begins to move upwardly. The solenoid 150 may incorporate time delay means so that it will hold the valve closed for a given time, or the cam 152 may be designed so that it will maintain the solenoid circuit closed for a predetermined time so as to achieve the time delay desired after the press ram begins to move upward before the die pad is returned to its extended position. Valve 102 is normally positioned in its open position by spring 104 as in FIG. 3.

in lieu of using a solenoid to close the valve 102 as schematically illustrated in PEG. 4, the valve 102 as illustrated in FIG. 5 may be shifted to its closed position by a piston 16% working in an air cylinder hi2 which is supplied with air under pressure from a suitable source of air pressure under the control of the rotary valve 164. The valve 1'64 may be a normally closed rotary valve whereby the cylinder 162 is normally ported to atmosphere through the port 166 because the valve arm 168 is normally positioned by the spring 170 was to establish communication between the atmospheric port 166 and the line 172 which connects the air cylinder 1&2 with the valve 1%. A cam 174 rotatable with the crank of the press engages the valve arm 168 periodically so that the valve 164 will connect line 172 with the line 176 leading to a source of air pressure for energizing the piston 16% so as to shift valve MP2 to its closed position before the press ram begins to open whereby the supply of hydraulic fluid under pressure from the tank 2%) to the end of the valve 32 may be delayed temporarily so as to delay opening of the valve 3% as in FIGS. 2 and 3.

in the modification of FIGS. 4 and 5, the valve 1112 may be a normally closed valve which would be opened by the solenoid or air cylinder means illustrated at the desired time in the cycle of press operation to permit opening of valve 36' under tank pressure when recharging of the cylinder 16 and return of piston 18 to its extended position are desired.

This application is a continuation-in-part of my copending application Serial No. 36,929 filed June 17, 1960, for Control for Die Pads and Presses, now Patent No. 3,077,344.

While I have illustrated and described preferred embodiments of my invention, it is understood that these are capable of modification, and I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. In a ram type press wherein a die pad engages the work and is retracted upon the closing of the press ram, a hydraulic cylinder and piston reacting on said die pad to resist such movement and to return the die pad to its extended position after opening of the press ram, a tank of hydraulic fluid under relatively low pressure, hydraulic fluid flow and pressure transmitting connections between said tank and cylinder for supplying hydraulic fluid under tank pressure to the cylinder when the tank pressure exceeds that of the cylinder, and normally closed valve means disposed in said hydraulic connections so as to provide a high pressure resistance to the discharge of hydraulic fluid from said cylinder during closing of the press ram, said valve means comprising a normally closed combined check and pressure relief valve having hydraulic pressure responsive surfaces exposed to the hydraulic fluid in said connections, said hydraulic connections including a fluid port forming a seat on which said valve seats in its closed position, a spring biasing said valve toward its seat, said valve being constructed so as to open by movement in one direction only when the effective pressure acting on the valve surface exposed to fluid pressure on the tank side of the valve exceeds the effective pressure on the opposite side of the valve exposed to fluid pressure on the cylinder side of the valve and means operable in response to an increase in the pressure on the hydraulic cylinder side of said valve substantially above tank pressure for suddenly reducing the pressure on at least one of said valve surfaces exposed to the pressure on the cylinder side of said valve so that resultant pressure on said valve surfaces will cause said valve to open and permit the flow of hydraulic fluid from the hydraulic cylinder side of the valve through said connections and valve toward said tank.

2. Apparatus according to claim 1 wherein said lastnamed means is responsive to a predetermined high pressure on the hydraulic cylinder side of said valve and comprises a normally closed valve-controlled passage around said Valve.

3. In a ram type press wherein a die pad engages the work and is retracted upon the closing of the press ram, a hydraulic cylinder and piston reacting on said die pad to resist such movement and to return the die pad to its extended position after opening of the press ram, a tank of hydraulic fluid under relatively low pressure, hydraulic fluid flow and pressure transmitting connections between said tank and cylinder for supplying hydraulic fluid to the latter, and normally closed valve means disposed in said hydraulic connections so as to provide a high pressure resistance to the discharge of hydraulic fluid from said cylinder during closing of the press ram, said valve means comprising a combined check and pressure relief valve having pressure responsive surfaces exposed to the hydraulic fluid in said connections, said hydraulic connections including a fluid port forming a seat on which said valve seats in its closed position, a spring biasing said valve toward its seat, said valve being constructed so as to open by movement in one direction only when the effective pressure acting on the valve surface exposed to fluid pressure on the tank side of the valve exceeds the effective pressure on the opposite side of the valve exposed to fluid pressure on the cylinder side of the valve and means responsive to a predetermined high pressure on the hydraulic cylinder side of said valve for relieving the pressure on at least one of said surfaces exposed to the hydraulic cylinder side of the valve so as to cause said valve to open and permit the flow of hydraulic fluid from the hydraulic cylinder side of the valve through said connections and valve toward said tank.

4. In a ram type press wherein a die pad engages the work and is retracted in response to the closing of the press ram, a hydraulic cylinder and piston reacting on said die pad to resist such movement and to return the die pad to its extended position after opening of the press ram, a source of hydraulic fluid, hydraulic fluid flow connections between said source and cylinder for supplying hydraulic fluid to the latter, and valve means disposed in said hydraulic connections so as to provide a high pressure resistance to the discharge of hydraulic fluid from said cylinder during closing of the press ram, said valve means comprising a valve having balanced pressure responsive surfaces exposed to the pressure of the hydraulic fluid in said cylinder and said source, means responsive to a predetermined high pressure on the hydraulic cylinder side of said valve for modifying the pressure on said surfaces during the final closing movement of the press ram so as to cause said valve to open and permit the flow of hydraulic fluid from the hydraulic cylinder side of the Valve through said connections and valve toward said source, means responsive to a low pressure condition on the hydraulic cylinder side of the valve for modifying the pressure on said valve surfaces after the closing movement of the press ram so as to cause said valve to open and permit the flow of hydraulic fluid from the source side of the valve through said valve toward said cylinder, and means for delaying the opening of said valve when closed upon opening of the press ram so as to delay the flow of hydraulic fluid from said source through said valve to said cylinder.

5. In a ram type press wherein a die engages the work and is retracted in response to the closing of the press ram, a hydraulic cylinder and piston reacting on said die to resist such movement and to return the die to its extended position after opening of the press ram, a tank of hydraulic fluid under relatively low pressure, hydraulic fluid flow and pressure transmitting connections between said tank and cylinder for supplying hydraulic fluid under tank pressure to the latter, and normally closed valve means disposed in said hydraulic connections so as to provide a high pressure resistance to the discharge of hydraulic fluid from said cylinder during closing of the press ram, said valve means comprising a normally closed piston valve having pressure responsive surfaces exposed to the hydraulic fluid in said connections on both sides of said valve, said hydraulic connections including a fluid port forming a seat on which said valve seats in its closed position, a spring biasing said valve toward its seat, said valve being constructed so as to open by movement in one direction only when the effective pressure acting on the valve surface exposed to fluid pressure on the tank side of the valve exceeds the effective pressure on the opposite side of the valve exposed to fluid pressure on the cylinder side of the valve, means operable when the pressure on the cylinder side of the valve falls below tank pressure to reduce the tank pressure on one of said surfaces so as to thereby cause said valve to open under tank pressure, and means responsive to a predetermined high pressure on the hydraulic cylinder side of said valve for reducing the pressure on at least one of said surfaces so as to cause said valve to open and permit the flow of hydraulic fluid from the hydraulic cylinder side of the valve through said connections and valve toward said tank.

6. In a ram type press wherein a die pad engages the work and is retracted upon the closing of the press ram, a hydraulic cylinder and piston reacting on said die pad to resist such movement and to return the die pad to its extended position after opening of the press ram, a tank of hydraulic fluid under relatively low pressure, hydraulic fluid flow and pressure transmitting connections between said tank and cylinder for supplying hydraulic fluid under pressure to the cylinder, and normally closed valve means in said hydraulic connections so as to provide a high pressure resistance to the discharge of hydraulic fluid from said cylinder during closing of the press ram, said valve means comprising a valve bore having a central port in one end wall thereof communicating with said tank and a lateral port in a side wall thereof communicating with said hydraulic cylinder, a combined check and pressure relief piston valve slidable in said bore between open and closed positions to control fluid flow through said bore between said ports, said piston valve in one position thereof seating on said end wall of said valve bore to close said port therein and prevent fluid flow between said ports, a valve cylinder, a piston movable with said piston valve and reciprocable in said valve cylinder, hydraulic fluid connections between said valve cylinder and said tank and hydraulic cylinder respectively, a reciprocable spool valve arranged to intersect said lastmentioned hydraulic fluid connections so that one of said connections is open while the other is closed and normally positioned so as to close the hydraulic fluid connection between said valve cylinder and said hydraulic cylinder, said spool valve having one end thereof exposed to the hydraulic fluid pressure in said hydraulic cylinder and the other end thereofexposed to the hydraulic fluid pressure in said tank so that .saidrspool valve will be positioned by the pressure of the fluid in the hydraulic cylinder when it is above tank pressure to open the hydraulic fluid connection between saidvalve cylinder and said tank and so that said spool valve will be positioned by the tank pressure when'it is.above.the pressure in said hydraulic cylinder to open the hydraulic fluid flow connection between said valve cylinder and said-hydraulic cylinder, a pressure relief passagebetween said tank and said valve bore on the side of the piston valve opposite said central port, the other side of said piston valvefacing and surrounding said central port being exposed to the pressure of the hydraulic fluid in said hydraulic cylinder when said piston valveis seated in position to close said central port, a restricted fluid flow passage between said hydraulic cylinder and said valve bore on the side of said piston valve opposite said central port, and a normally closed pilot relief valve in said pressure relief passage arranged to be opened by the hydraulic fluid pressure on the hydraulic cylinder side of said piston valve when said pressure rises above tank pressure due to closing of the press ram so as to cause said piston valve to shift to its open position and permit the flow of hydraulic fluid between said valve bore ports from the hydraulic cylinder side of said piston valve to the tank side thereof.

7. In a ram type press wherein a die pad engages the work and is retracted upon the closing of the press ram, a hydraulic cylinder and piston reacting on said die pad to resist such movement and to return the die pad to its extended position after opening of the press ram, a tank of hydraulic fluid under relatively low pressure, hydraulic fluid flow and pressure transmitting connections between said tank and cylinder for supplying hydraulic fluid under pressure to the cylinder, and valve means in said hydraulic connections so as to provide a high pressure resistance to the discharge of hydraulic fluid from said cylinder during closing of the press ram, said valve means comprising a valve bore having a central port in one end wall thereof and a lateral port in a side wall thereof, a piston valve slidable in said bore between open and closed positions to control fluid flow through said bore between said ports, said piston valve in one position thereof seating on said end wall of said valve bore to close said port therein and prevent fluid flow between said ports, a valve cylinder, a piston movable with said piston valve and reciprocable in said valve cylinder, hydraulic fluid connections between said valve cylinder and said tank and hydraulic cylinder respectively, a control valve controlling fluid flow through said last-mentioned hydraulic fluid connections so that one of said connections is open while the other is closed and normally positioned so as to close the hydraulic fluid connection between said valve cylinder and said hydraulic cylinder, said control valve being subject to the hydraulic fluid pressure in said hydraulic cylinder and in said tank so that said control valve will be positioned by the pressure of the fluid in the hydraulic cylinder when it is above tank pressure to open the hydraulic fluid connection between said valve cylinder and said tank and so that said control valve will be positioned by the tank pressure when it is above the pressure in said hydraulic cylinder to open the hydraulic fluid flow connection between said valve cylinder and said hydraulic cylinder, a pressure relief passage between said tank and said valve bore on the side of the piston valve opposite said central port, the other side of said piston valve having a surface exposed to the pressure of the hydraulic fluid in said hydraulic cylinder when said piston valve is seated in position to close said central port, a restricted flow passage between said hydraulic cylinder and said valve bore on the side of said piston valve opposite said central port, and a normally closed pilot relief valve in said pressure relief passage arranged to be opened by the hydraulic fluid pressure on the hydraulic cylinder side of said piston valve 10 when said pressure risessubstantially above tank pressure due to closing of the press ram so as to cause said piston valve to vshift to its open position andpermit the flow of hydraulic fluid between said valve bore ports from the hydraulic cylinder side of said piston valve to the tank side thereof.

8. Apparatus according to claim 7 including means responsive to an increase in pressure on the hydraulic cylinder side of said piston valve for'holding said control valve in a position to close the hydraulic fluid connection between said valve cylinder and tank to delay opening movement of said piston valve after-the press ram begins to open.

9. In a ram type press wherein a die pad 'engages'the work and is retracted upon the closing of the press ram, ashydraulic cylinder andpiston reacting on said die'pad to resist such movement and to return the die pad to its extended position after opening of the press ram, a tank of hydraulic fluid under relatively low pressure, hydraulic fluid flow and pressure transmitting connections between said tank and hydraulic cylinder for supplying hydraulic fluid under pressure to the cylinder, and valve means in said hydraulic connections to provide a high pressure resistance to the discharge of hydraulic fluid from said cylinder during closing of the press ram, said valve means comprising a valve bore having a central port in one end wall thereof and a lateral port in a side wall thereof, a piston valve slidable in said bore between open and closed positions to control fluid flow through said bore between said ports, said piston valve in one position thereof seating on said end wall of said valve bore to close said port therein and prevent fluid flow between said ports, a spring biasing said piston valve to close said port, said piston valve having balanced pressure responsive surfaces exposed to the hydraulic fluid in said connections, a valve cylinder, a piston movable with said piston valve and reciprocable in said valve cylinder, hydraulic fluid connections between said valve cylinder and said tank and hydraulic cylinder respectively, a control valve controlling fluid flow through said last-mentioned hydraulic fluid connections so that one of said connections is open while the other is closed and normally positioned so as to close the hydraulic fluid connection between said valve cylinder and said hydrauic cylinder, said control valve being subject to the hydraulic fluid pressure in said hydraulic cylinder and in said tank so that said control valve will be positioned by the pressure of the fluid in the hydraulic cylinder when it is above tank pressure to open the hydraulic fluid connection between said valve cylinder and said tank and so that said control valve will be positioned by the tank pressure when it is above the pressure in said hydraulic cylinder to open the hydraulic fluid flow connection between said valve cylinder and said hydraulic cylinder, a pressure relief passage between said tank and said valve bore on the side of the piston valve opposite said central port, the other side of said piston valve having a surface exposed to the pressure of the hydraulic fluid in said hydraulic cylinder when said piston valve is seated in position to close said central port, a restricted flow passage between said hydraulic cylinder and said valve bore on the side of said piston valve opposite said central port, and a normally closed pilot relief valve in said pressure relief passage arranged to be opened by the hydraulic fluid pressure on the hydraulic cylinder side of said piston valve when said pressure rises substantially above tank pressure due to closing of the press ram so as to cause said piston valve to shift to its open position and permit the flow of hydraulic fluid between said valve bore ports from the hydraulic cylinder side of said piston valve to the tank side thereof.

10. Apparatus according to claim 6 wherein said piston valve includes a pilot slidable in said central port in said end wall of said valve bore and said pilot is provided with V-shaped notches which form fluid flow ports as the piston valve opens.

11. In a ram type press wherein a die pad engages the work and is retracted upon the closing of the press ram, a hydraulic cylinder and piston reacting on said die pad to resist such movement and to return the die pad to its extended position after opening of the press ram, a tank of hydraulic fluid under relatively low pressure, hydraulic fluid flow and pressure transmitting connections between said tank and cylinder for supplying hydraulic fluid to the latter, and normally closed valve means disposed in said hydraulic connections so as to provide a high pressure resistance to the discharge of hydraulic fluid from said cylinder during closing of the press ram, said valve means comprising a combined check and pressure relief valve having pressure responsive surfaces exposed to the hydraulic fluid in said connections, means responsive to a predetermined high pressure on the hydraulic cylinder side of said valve for relieving the pressure on at least one of said surfaces so as to cause said valve to open and permit the flow of hydraulic fluid from the hydraulic cylinder side of the valve through said connections and valve toward said tank, and means for holding said valve closed temporarily for preventing the flow of hydraulic fluid from said tank through said connections and valve toward said cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 1,577,446 Brown Mar. 23, 1926 1,848,383 Rode Mar. 8, 1932 2,699,178 Adams et a1. Jan. 11, 1955 2,901,238 Williamson Aug. 25, 1959 

1. IN A RAM TYPE PRESS WHEREIN A DIE PAD ENGAGES THE WORK AND IS RETRACTED UPON THE CLOSING OF THE PRESS RAM, A HYDRAULIC CYLINDER AND PISTON REACTING ON SAID DIE PAD TO RESIST SUCH MOVEMENT AND TO RETURN THE DIE PAD TO ITS EXTENDED POSITION AFTER OPENING OF THE PRESS RAM, A TANK OF HYDRAULIC FLUID UNDER RELATIVELY LOW PRESSURE, HYDRAULIC FLUID FLOW AND PRESSURE TRANSMITTING CONNECTIONS BETWEEN SAID TANK AND CYLINDER FOR SUPPLYING HYDRAULIC FLUID UNDER TANK PRESSURE TO THE CYLINDER WHEN THE TANK PRESSURE EXCEEDS THAT OF THE CYLINDER, AND NORMALLY CLOSED VALVE MEANS DISPOSED IN SAID HYDRAULIC CONNECTIONS SO AS TO PROVIDE A HIGH PRESSURE RESISTANCE TO THE DISCHARGE OF HYDRAULIC FLUID FROM SAID CYLINDER DURING CLOSING OF THE PRESS RAM, SAID VALVE MEANS COMPRISING A NORMALLY CLOSED COMBINED CHECK AND PRESSURE RELIEF VALVE HAVING HYDRAULIC PRESSURE RESPONSIVE SURFACES EXPOSED TO THE HYDRAULIC FLUID IN SAID CONNECTIONS, SAID HYDRAULIC CONNECTIONS INCLUDING A FLUID PORT FORMING A SEAT ON WHICH SAID VALVE SEATS IN ITS CLOSED POSITION, A SPRING BIASING SAID VALVE TOWARD ITS SEAT, SAID VALVE BEING CONSTRUCTED SO AS TO OPEN BY MOVEMENT IN ONE DIRECTION ONLY WHEN THE EFFECTIVE PRESSURE ACTING THE VALVE SURFACE EXPOSED TO FLUID PRESSURE ON THE TANK SIDE OF THE VALVE EXCEEDS THE EFFECTIVE PRESSURE ON THE OPPOSITE SIDE OF THE VALVE EXPOSED TO FLUID PRESSURE ON THE CYLINDER SIDE OF THE VALVE AND MEANS OPERABLE IN RESPONSE TO AN INCREASE IN THE PRESSURE ON THE HYDRAULIC CYLINDER SIDE OF SAID VALVE SUBSTANTIALLY ABOVE TANK PRESSURE FOR SUDDENLY REDUCING THE PRESSURE ON AT LEAST ONE OF SAID VALVE SURFACES EXPOSED TO THE PRESSURE ON THE CYLINDER SIDE OF SAID VALVE SO THAT RESULTANT PRESSURE ON SAID VALVE SURFACES WILL CAUSE SAID VALVE TO OPEN AND PERMIT THE FLOW OF HYDRAULIC FLUID FROM THE HYDRAULIC CYLINDER SIDE OF THE VALVE THROUGH SAID CONNECTIONS AND VALVE TOWARD SAID TANK. 